Intro Animal Evolution and Development

All Animals have what characteristics?

multicellular, lack cell walls, heterotrophs

External Fertilization vs Internal Fertilization

External fertilization occurs outside of the female body while internal fertilization occurs inside of the female body.

Hox Genes

control the body plan along the anterior-posterior axis of an embryo.

Properties of Choanoflagellates

• Closest living ancestor to humans

• Under eukaryotic supergroup Opisthokonta

• Many are sessile, some can swim

• A single flagellum and a collar of microvilli attached to the cell body.

The Protists (Kingdom Protista)

Eukaryotic, aerobic, unicellular microorganisms

Characteristics of the Protozoans

• without a cell wall

• heterotrophy

• motillity

When did animal life begin on Earth?

600 mya

Cambrian Explosion

Many phyla appeared (533-525 mya)

Amniotic Egg

Adaptation that prevented egg from drying out. Allowed animals to be terrestrial for entire life. (300 mya)

How do we classify animals?

• tissue types

• morphological data (symmetry)

• Embryological data (development processes)

• Genetic Data (DNA, mRNA, Proteins)

Development

Describes the progressive changes in an individual from it’s beginning to maturity.

Stages of embryonic development

1. Gamete formation

2. fertilization

3. cleavage

4. gastrulation

5. organogenesis

6. growth

Gametogenesis

the process for which gametes are produced.

Spermatogenesis

Spermatogenesis is the process by which sperm cells are produced in the testes. Sperm are haploid.

Oogenesis

Oogenesis is the process by which a female's ovaries produce ova, or eggs, that are capable of developing into an embryo after fertilization. Oocytes are haploid.

Haploid

Single set of unpaired chromosomes.

Fertilization

contact and recognition between egg and sperm . Sperm and egg fuse diploid zygote.

Cleavage

Repeated divisions of zygote, converting a single large cell into many smaller cells called blastomeres. Zygote cells perform cleavage according to symmetry.

Morula

Mass of blastomeres

Spiral Cleavage

• occurs in most protostomes

• Cleavage planes are not parallel or perpendicular to the animal-vegetal axis of the egg, but instead in a spiral arrangement.

• Mosaic Development

Examples of protostomes with spiral cleavage

• Platyhelminthes (flatworms)

• Annelids (earthworms)

• Molluscs (snails, squid)

Mosaic Development

need all cells for growth

goes with spiral cleavage

Radial Cleavage

The cleavage planes are either parallel or perpendicular to the vertical axis of the embryo.

Examples of Deuterostomes with Radial Cleavage

• Echinoderms

• Hemichordates (acorn worms)

• Chordates

Regulative Development

can divide and form normal larva

goes with radial cleavage

Blastula

A sphere of cells

a hollow ball of cells

Germ Layers

layers of cells

Gastrulation

an area of the blastula folds inward, or invaginates, creating in the process a structure called the gastrula.

converts the spherical blastula into a two-or three- layered embryo

Endoderm

Inner layer of cells in a blastula. Lines the primitive digestive tract.

Ectoderm

outer layer of the blastula. Covers surface of embryo and differentiates into the epidermis and nervous system.

Archenteron

internal cavity formed by invagination

Blastopore

Opening formed during gastrulation in an embryo.

Blastocoel

the internal cavity within a blastula

Coeloblastula

a type of blastula with a blastocoel cavity

Diploblastic

Organisms with two germ layers: the ectoderm and endoderm.

Diploblastic animals have radial symmetry

Triploblastic

Animals with a 3rd germ layer, the mesoderm. The mesoderm is often derived from the endoderm.

Protostomes (coelomates)

Cells arise from ventral area and proliferate into blastocoel

Deuterostomes

Central region of archenteron wall pushes outward

Coelom

a cavity surrounded by mesoderm formed by schizocoely or enterocoely

Schizocoely

Mesoderm surrounds gut and splits open to form coelom

• found in schizocoelous coelomates in protostomes

• spiral cleavage

Protostomes

the blastopore becomes the mouth. Originate from spiral cleavage, mosaic (determinate) development.

• Acoelomates

• Pseudocoelomates

• Schizocoelous coelomates

Enterocoely

mesoderm and coelom are made at the same time

• in deuterostomes

• radial cleavage

Deuterostomes

mouth is newly formed. Anus often is derived (but not always) from the blastopore. Originate from radial cleavage.

• anus is formed from blastopore (or not!)

Diploblastic

animals do not have organs

Two tissues: epidermis and gastrodermis

gastrodermis: endoderm in the context of cnidarians

Organogenesis

the differentiation of the three embryogenic layers into tissues and organs.

Organogenesis: Ectoderm

Nervous system and outer epithelium (skin)

Organogenesis: Endoderm

Digestive tube (gut) and gill arches

Gill arches

In fish:

gills and supportive structures

In humans:

involved in the formation of jaws, inner ear, tonsils, parathyroid glands and thymus

Organogenesis: mesoderm

support, movement, circulatory system, urinary and reproductive organs.

Factors determined by growth

genes, nutrients, environment